A. The Pressure Shoe Feature
Finishing machines utilizing abrasive heads, such as wide-belt sanding machines, knife planers, molding heads, shapers and rotary shaping tools normally include pivotally adjustable pressure shoes mounted in opposed relationship to the surface of the conveyor belt and adjacent the finishing head along both the infeed and outfeed sides of the head. Pressure shoes in general are well known in the prior art, with examples of two such devices being disclosed in U.S. Pat. No. 3,782,044 to Olin and U.S. Pat. No. 4,594,815 to Mickelson et al, each of which is assigned to the same assignee as the present invention, and with the disclosures of each being incorporated herein by reference. In wide-belt abrasive sanding and finishing machines, one or more working heads are typically provided. Each head typically comprises an endless abrasive belt trained about two or more drums or rollers, with one or more of the drums being power driven and with the others normally being idlers. The ends of the drums have axially positioned concentric shafts which extend outwardly from the ends and which are typically journaled and mounted for rotation within the frame of the apparatus. The drums typically have parallelly disposed axes which are adapted for appropriate adjustment of position, with one drum typically being arranged to control belt trackings.
In operation of these finishing machines, workpieces are normally fed into the machine and carried to the work station along the upper flight of a horizontally disposed endless belt conveyor. The abrasive heads are positioned in spaced relationship to the top surface of the conveyor belt so as to form one or more working stations along the length of the belt. While abrasive heads are normally positioned to come into contact and treat the top surface of the workpiece, they are sometimes positioned to come into contact with and treat the bottom surface of the workpiece as well. Bottom-head machines require pressure shoes the same as top-head machines, it being understood, therefore, that the disclosure of operation of top-head machines is exemplary only.
Workpieces arrive at the machine with a certain randomness of thickness dimension. Considering the dimensional tolerances involved, and considering further the value of the workpieces at this stage of their processing, it becomes important for the apparatus to create a working balance between each of the individual sequentially positioned work stations so as to ensure that each of the individual abrasive belts will be operating so as to treat the workpiece so as to replace the qualified scratch created at the prior station with a finer qualified scratch which may be effectively treated at the next succeeding station. Additionally, the individual abrasive belts will be operating within the working parameters of the working grit or mineral which it carries on its surface. Furthermore, it will be appreciated that the apparatus must be capable for use with a variety of woods, varying from soft to hard, and with each variety possessing individual abrading or mechanical response properties. It is, therefore, important to provide an apparatus which is capable of responding to the individual requirements and needs of the various woods involved, while permitting effective use of the apparatus with each of these different wood varieties so as to replace an incoming qualified scratch pattern with an outgoing and finer qualified scratch pattern.
The conveyor belt assembly may be typically vertically adjustable either toward or away from the abrasive belt assemblies. In certain machines, the conveyor belt may be designed so as to provide a floating bed arrangement, it being understood that the system of the present invention is adaptable for use in combination with either types of assemblies. One adjustable conveyor which may be utilized with wide-belt sanding apparatus of the present invention are disclosed in U.S. Pat. No. 3,832,808, and reference is made to the disclosure in that patent for the details of such an adjustable conveyor design.
The automatic setup system or feature of the present invention is arranged to provide for substantially automatic adjustment of the machine so that, following the initial setup operation, finished workpieces of consistent finish and uniform thickness will be produced. The arrangement of the present invention is further designed to compensate for any springiness in the machine, thereby achieving greater consistency and uniformity in thickness of the finished workpieces.
As indicated above, in a typical abrasive surface treatment machine, the upper span or flight of the conveyor belt cooperates with a series of pressure shoes or pinch rollers which press the workpieces against the conveyor belt while the workpieces are being fed through the working station of the machine. These pressure shoes or rollers are adjustably positioned relative to a plane parallel to and generally tangent to the work contacting surface of the heads. These pressure shoes or pinch rollers are pivotally mounted to control the path of the workpiece as it enters, passes through, and exits the working zone defined beneath the work contacting surface of the surfacing head. When properly set and adjusted, these devices assure smooth and consistent feeding of the workpiece through the machining process and assist in achieving a smooth and consistent surface on the workpiece. If the pressure shoes or pinch rolls are positioned where excessive force is applied, passage of the workpiece is restricted and marks or blemishes may be produced on the surface of the workpiece or the workpiece may be stopped entirely. If the adjustment of the pressure shoes is such that insufficient force is being applied, the workpiece may either hesitate or move intermittently, thereby producing a rippled or washboard-like surface due to inconsistent motion, with the shoes having little effect on machine operation. A feature of the arrangement of the present invention has been found to enhance the consistency of force adjustment for the pressure shoes, thereby enhancing control of workpiece motion and accordingly the quality and consistency of the surface of the finished workpiece.
In the past, pressure shoes and/or rollers have been provided with travel limiting stops, typically comprised of either a rigid system or a modestly flexible system with only limited motion possible. A typical rigid system is disclosed in U.S. Pat. No. 3,782,044 to Olin. Such a rigid system may simply include a bolt that passes freely through a bracket and is threaded into the upper portion of the shoe. Lock nuts secure the bolt in a rigid position to secure the shoe against loss of adjustment. In a system which provides for flexible mounting of the shoe with limited travel, a spring or pneumatic device may be implemented to provide a mechanical bias with yieldable travel. In the latter machines, the machine operator typically accomplishes the setup operation by what is known in the art as "feel". In this arrangement, the operator simply moves a workpiece through the machine and compares the magnitude of the "drag" which he senses manually against that of a standard setup spool or gauge. (See FIG. 4). In this manner, the pressure shoe or roller is adjustably positioned relative to a plane which is tangent to the apex point or workpiece engaging surface of the abrasive head positioned above and in spaced relationship to the load bearing surface of the conveyor belt.
One anomaly of drum-head wide belt sanders is that the surface of the drum is typically provided with a layer of rubber or other resilient material which deforms and deflects during the abrasive finishing process. The magnitude of deformation is in direct response to the downward forces involved in the specific abrasive operation. The deflection of the resilient material (typically rubber) and the characteristic springiness of the overall machine are parameters which cannot be measured and given an absolute value. These undefinable parameters make the setup process subject to a certain amount of guesswork, and accordingly require evaluation of empirical data gathered through trial and error operations. As a result, a pressure shoe or roller may be set a few thousandths of an inch higher or lower than the apex of the surfacing head based on empirical evaluations, the success of which are subject to the training, experience and skill level of the setup person. The empirical evaluation process normally requires several independent tests in order to permit the setup person to make those numerous slight adjustments which lead to desired results. The time needed depends upon the accuracy required and also upon the specific results desired. Accordingly, accurate, and repeatable machine setup is difficult to perform, and the setup operation is frequently labor-intensive and time-consuming.
As an additional complicating factor, as the abrasive surface of the abrasive belt or other surfacing head wears, the space or gap between the apex of the surfacing head and the conveyor belt surface is subject to change. Thus, periodic readjustment of the pressure shoe or roller have typically been required in order to consistently maintain the desired spaced relationship between a plane extending tangent to the apex of the surfacing head and the plane of the working surface of the pressure shoes. While initial setups have normally been performed by positioning the pressure shoe relative to the abrasive surfacing head, subsequent readjustment to accommodate for wear is usually performed by adjustably positioning the abrasive surfacing head relative to the working surface of the pressure shoe or pinch roll. Such setup operations and readjustment operations have similarly been undertaken with machines having abrasive heads other than widebelt sanders, such as knife planers or the like.
The data created from the making of such adjustments is gathered, and transferred to a memory bank such as a microprocessor. Additional data, including power requirements for the operation of individual heads, the varieties of wood being treated, the thickness of workpieces exiting each work station, and thickness measurements and tolerances for incoming workpieces are representative of other data which is to be included in the processor. Such data is useful in the proper positioning of the shoes as well as the individual abrasive surfacing heads, including the drum head wide belt sanders. Thus, the system maintains stock removal at the optimum level so as to completely replace the scratch pattern created at the abrasive head in the prior work station. Excessive stock removal reduces the abrasive belt life and causes excessive loading of the drive, resulting in a requirement for more frequent adjustments than otherwise would be necessary. When an insufficient amount of stock is removed, the head may fail to completely replace the scratch pattern created from the abrasive head in the prior work station.
Accordingly, the head in each work station removes only the amount of stock needed to remove the scratch pattern produced at the prior work station, replacing it with a scratch pattern from the current head. By way of example, at one station, a #36 grit scratch pattern is removed by replacing it with a #50 grit scratch pattern. At the next succeeding station, the #50 grit scratch pattern is removed, and replaced with a #100 grit scratch pattern, etc. In multiple station systems, each grit in the sequence is finer than its predecessor, it being understood that as the grit becomes smaller in size, its capability of stock removal decreases. Thus, multiple stations are required in order to achieve an appropriate and acceptable surface finish on the workpiece.